Re: [fpc-pascal] Loading PNG files as OpenGL textures

[Ryan Joseph]

> On Oct 12, 2015, at 10:57 AM, Anthony Walter <sys...@gmail.com> wrote:
> 
> I tend to use OS core elements or well known open source libraries for a few 
> reasons.
> 
> 1) less code compiled and small programs
> 2) superior performance
> 3) more features
> 
> Example: When loading hundreds of textures you bet the Apple Quartz graphics 
> libs are faster and more reliable. Same goes to WIC on Windows and Cario on 
> linux.
> 

So your advice would be to keep my Apple libraries I use on Mac and something 
else for Windows? What would be the equivalent libraries on Windows for CGImage 
and CGBitmapContext be?

Loading PNG’s into a bitmap seems like a pretty thing for single unit but I 
could do the native route also if it was easier. I just wanted to get started 
on cross platform basically and I’m looking for the easiest strategy.


Here’s an example function to load a texture on Mac (given a CGImageRef you 
load from CGImageCreateWithURL). Pretty easy using Apple frameworks and I 
assume those would have some FPC RTL equivalents.

function GenerateTextureFromImage (image: CGImageRef): GLuint;
var
        textureWidth, textureHeight: integer;
        textureName: GLuint;
        bounds: CGRect;
        bitmapData: pointer;
        colorSpace: CGColorSpaceRef;
        context: CGContextRef;
begin
        result := 0;
        
        // generate texture
        textureWidth := CGImageGetWidth(image);
        textureHeight := CGImageGetHeight(image);
        bounds := CGRectMake(0, 0, textureWidth, textureHeight);
        bitmapData := GetMem(textureHeight * (textureWidth * 4));
        
        if bitmapData <> nil then
                begin
                        colorSpace := CGColorSpaceCreateDeviceRGB;
                  context := CGBitmapContextCreate(bitmapData, textureWidth, 
textureHeight, 8, 4 * textureWidth, colorSpace, kCGImageAlphaPremultipliedLast);

                        if context <> nil then
                                begin
                                        CGContextFlipVertically(context, 
bounds);
                                        CGContextClearRect(context, bounds);
                                        CGContextDrawImage(context, bounds, 
image);
                                        
                                        glGenTextures(1, @result);
                                        glBindTexture(GL_TEXTURE_2D, result);
                                        glTexParameteri(GL_TEXTURE_2D, 
GL_GENERATE_MIPMAP, GL_TRUE);
                                        glTexImage2D(GL_TEXTURE_2D, 0, GL_RGBA, 
textureWidth, textureHeight, 0, GL_RGBA, GL_UNSIGNED_BYTE, bitmapData);

                                        //writeln('generated texture ', result, 
' (', textureWidth, 'x', textureHeight,')');
                                        CGContextRelease(context);
                                end;

                        FreeMemory(bitmapData);
                        CFRelease(colorSpace);
                end;
end;


Regards,
        Ryan Joseph

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